Investigation into alternative wastewater treatments options for a large beef processing facility

Summary

The Teys Naracoorte beef processing facility currently operates an open anaerobic lagoon and a downstream aerobic lagoon to biologically treat its wastewater. These two lagoons have treated the wastewater for a number of years, but recent wastewater samples out of the aerobic lagoon indicate that treatment performance may be falling in these ponds. At the same time, the facility has experienced a significant increase in the cost of electricity and natural gas. The purpose of this project was to evaluate the condition of the existing system and investigate the feasibility of a number of different wastewater treatment options and their potential for biogas generation and use for energy displacement.

A sludge survey of both the anaerobic and aerobic lagoons was undertaken by Johns Environmental. This revealed that the anaerobic lagoon has lost approximately 40% (9.3ML), and the aerobic lagoon 27% (54ML) of their working volume. The loss is due to a combination of a surface crust (especially in the anaerobic lagoon) and an accumulation of a sludge layer in both ponds.
In the anaerobic lagoon, the crust and sludge layers appear to comprise a combination of paunch solids and oil & grease. This suggests that the primary treatment system is not working properly to capture excess paunch solids. The conclusion of the sludge survey was that the anaerobic pond has a limited remaining lifetime, and if it is not replaced shortly even greater quantities of solids may be carried over into the aerobic pond, further reducing its remaining lifetime. It is recommended that the anaerobic lagoon be replaced as part of Stage 2 of this project.

A geotechnical survey was performed by FMG Engineering in June 2017 to determine the integrity of the existing walls of the anaerobic and aerobic lagoons as well as the suitability of the surrounding ground for the construction of a new anaerobic lagoon. This included investigation of soil conditions in two decommissioned lagoons to the east of the existing anaerobic lagoon and also in an area to the north of these lagoons ("new area").

The survey confirmed the surface geology of the two sites being considered for a new anaerobic lagoon. Essentially it found that there is an area of Gambier limestone in the east part of these sites adjacent to Parilla Sand to the west. No groundwater was observed in any of the test pits or boreholes, although this does not exclude the possibility of localised areas of perched watertable.

The geotechnical report contains additional test information concerning the properties of the soils and sub-soils in the areas investigated. A visual examination of the walls of the existing anaerobic lagoon suggested some damage of concern including tree root penetration, and erosion with particular damage to the northern wall.

A cost benefit analysis (CBA) was completed to calculate the feasibility of constructing a new, covered anaerobic lagoon (CAL) with and without biogas combustion in a cogeneration system for electricity production. The CBA also looked at whether it was beneficial to undertake such an upgrade now, or delay capital expenditure for a period of 5 years.

The CBA concluded that construction of a new CAL is advisable sooner rather than later (taken as 5 years’ delay) due to the considerable cost to remove sludge discharged from the existing anaerobic pond which is accumulating in the eastern deeper part of the aerobic dam where both inlet and outlet are located. It is probable that the sludge accumulation in the aerobic dam will contribute to non-compliant treated effluent and potentially odour if the quantity discharged from the anaerobic pond is not reduced.

The CBA also showed that construction of a CAL with cogeneration would displace electricity, repaying a portion (but not all) of the capital expenditure. However, considering that an upgrade to the wastewater treatment plant is necessary due to the diminishing lifetime of the existing lagoons, the displacement of mains electricity with biogas is still quite attractive. This is especially the case considering the uncertainty in the Australian energy market. South Australia has experienced a considerable rise in the cost of electricity and natural gas in the past 2 years. Having access to an on-site source of electricity also provides the facility with some security and reduced reliance on a potentially unreliable mains electricity network.

If Teys Australia are able to defray the capital cost of the cogeneration system through external funding, the project is financially more attractive than the construction of a new CAL without a cogeneration system.

Considering all of this as well as the cost of remedial works required if the upgrade were to be delayed 5 years from now as well as the implications of the time value of money, our recommendation is that it is best to commence the upgrade as soon as possible and that the combination of a new CAL with cogeneration provides the most economic outcome.